Metallographic diagram of 50 steel (hot rolled)

Introduction

20Mn50 steel is a medium carbon, high manganese, low alloy steel. It is heat treated to produce a variety of properties, such as improved toughness, ductility, strength, hardness, and wear resistance. It is commonly used in tools, dies, and machine parts. In this study, a Metallographic Analysis of 20Mn50 Steel is presented.

Metallography

Metallography is an examination of the internal structure of a metal. It is a visual representation of the microstructure of the metal in question and provides an understanding of its mechanical and physical properties. Metallographic analysis involves the inspection of the sectioned component, including surface preparation, selection of the optical and electron microscopes, selection of the material for hardening, preparation of specimen mountings,photomicrography, and analysis of the microstructure.

Materials and Methods

The analysis of 20Mn50 Steel entailed the collection of a one-inch wide sample from a hot-rolled flat bar. The sample was surface ground with 400 and 600 grit sandpaper and then polished with a 1 micron diamond polishing compound. After cleaning, the sample was mounted on a 1-inch sample holder and cut into slices for further examination.

The microstructure of the 20Mn50 steel sample was examined using optical and scanning electron microscopy (SEM). The optical microscope was used to examine the overall grain structure and then the sample was further scanned using the SEM which gave a more in depth analysis. The metallurgical examination revealed the phases and microstructure or 20Mn50 steel. The microstructure, including grain size and grain boundaries were identified and compared to the theoretical prediction.

Results and Discussion

The metallurgical examination of the 20Mn50 steel showed that it is composed of a ferrite matrix with some martensite and trace amounts of unit figures and pearlite present. The ferrite grains were identified to be of size 10 micron with some finer grain sizes present. These grains had a predominately uniform characteristic with some areas showing evidence of inter–granular boundaries.

The martensite and pearlite phases were observed at the grain boundaries and had a face–centered cubic crystal lattice structure. Also observed were some unit figures which showed small regions of crystalline twinning along with some trace amounts of second–phase particles.

Conclusion

The Metallographic Analysis of 20Mn50 Steel provided a visual representation of the microstructure of the alloy and showed that it consisted of a ferrite matrix with some martensite, pearlite, and unit figures present. The ferrite grains were identified to be of size 10 micron with some finer grain sizes present. Also observed were some unit figures which showed small regions of crystalline twinning along with some trace amounts of second–phase particles. The microstructure analysis revealed that the properties of 20Mn50 steel are consistent with those expected for this grade of steel.

Microstructure of 45# Steel

45# steel is a kind of hot rolled steel. It is composed of carbon, manganese, silicon, sulfur, phosphorus and other components. The composition of 45#steel is as follows: carbon 0.43%, manganese 0.50%, silicon 0.20%, sulfur 0.03%, phosphorus 0.02%.

The microstructure of 45#steel is pearlite, and the ferrite phase has a higher degree of freedom to move around the pearlite needle. The amount of pearlite network is relatively small, as a small needle or thin strip, the spacing of pearlite is large. The grain size of ferrite is mainly lower than 3μm, the degree of grain refinement is low, and the coarse grain and small grain corner are relatively uniform.

On the metallographic section of 45# steel, the pearlite network is formed by ferrite and cementite distribution in the scale interval, and the cementite and the ferrite in the scale interval are staggered with each other. On the surface of the pearlite network, there are some ferrite grains, and the ferrite grains between the pearlite network also have some islands. There are also some MnS inclusions.

In summary, the microstructure of 45# steel is mainly pearlite. It is composed of cementite and ferrite grains, which are spaced with each other, and ferrite and MnS inclusions dispersed between them. Its grain size is mainly lower than 3μm.